1. Field of the Invention
The present invention relates to a modulation and demodulation system, a modulator, a demodulator and a phase modulation method and a phase demodulation method used therefor, and in particular, to encoding for minimizing a bit error per a symbol error in a modulation demodulation method for transmitting a binary signal of predetermined length b correspondingly to a senary phase signal of predetermined length m against a predetermined integral value N other than power of 2, and encoding for minimizing the bit error per the symbol error in the modulation and demodulation method for transmitting a binary signal of length “5” correspondingly to a senary phase signal of length “2.”
2. Description of the Prior Art
Conventionally, 2n phase modulation is used with n as a positive integer in two-phase phase modulation (Binary Phase Shift Keying: BPSK), four-phase phase modulation (Quadrature Phase Shift Keying: QPSK), eight-phase phase modulation and so on especially in the cases of digital phase modulation used for digital microwave communication, satellite communication, mobile communication and so on.
As for the digital microwave communication, satellite communication, mobile communication and so on, the 2n phase modulation is generally used with n as a positive integer in the two-phase phase modulation, four-phase phase modulation, eight-phase phase modulation and so on for the reason of simplicity of circuitry and consistency with a binary signal.
To meet requests for effective utilization of transmission power and frequencies, the 2n phase modulation method is generally used as a modulation technology (refer to “Modulation and Demodulation of Digital Wireless Communication” (Yoichi Saito, Institute of Electronics, Information and Communication Engineers, February 1996), for instance). It is possible, as to these modulation methods, to minimize a bit error per symbol error by using the encoding well known as gray encoding.
Difficulties in implementation due to complicated circuitry are gradually alleviated by advancements in integrated circuit technology in recent years. Furthermore, the requests for effective utilization of frequencies and transmission power are becoming stronger.
As for a phase shift keying technology not rendering a phase number as 2n, propositions are made as to configurations of three-phase, five-phase, six-phase and seven-phase phase shift keying modulations (refer to S. Noda, K. Nakamura and K. Koga, “Performance and application of PSK modulation whose number of phases is not a power of 2,” Proceeding of ISITA' 02, Xi' an, pp239 to 242, October 2002., for instance). In the case of the three-phase phase modulation, disclosure is made as to a configuration method thereof (refer to Japanese Patent Laid-Open Nos. 53-147454, 2003-060721, 2003-110644, for instance) and an encoding method for minimizing a bit error (refer to Japanese Patent Laid-Open No. 2004-129013 and S. Noda, K. Nakamura and K. Koga, “Performance and application of PSK modulation whose number of phases is not a power of 2,” Proceeding of ISITA' 02, Xi' an, pp239 to 242, October 2002. , for instance). Disclosure is also made as to a technology relating to error-correction coding of the six-phase phase modulation (refer to Japanese Patent Laid-Open Nos. 2003-204365 and 2003-204316, for instance).
Furthermore, regarding the three-phase phase modulation, disclosure is made as to the configuration method (refer to Japanese Patent Laid-Open Nos. 53-147454, 2003-060721, 2003-110644 and Japanese Patent Laid-Open No. 53-147454, 2003-060721, 2003-110644, for instance) and the encoding method for minimizing a bit error (refer to Japanese Patent Laid-Open No. 2004-129013 and S. Noda, K. Nakamura and K. Koga, “Performance and application of PSK modulation whose number of phases is not a power of 2,” Proceeding of ISITA' 02, Xi' an, pp239 to 242, October 2002., for instance). A proposition is also made by the applicant hereof as to an encoding method for improving the error rate of the six-phase phase modulation.
For this reason, in the case of n=2 in the 2n phase modulation for instance, it is the four-phase phase modulation. To minimize the bit error per symbol error, it requires encoding for minimizing the Hamming distance between adjacent signal points considering that errors predominantly occur at the adjacent signal points under a thermal noise environment. The gray encoding is well known for the sake of meeting this request.
In the case of applying the gray encoding to the six-phase phase modulation, however, there is a problem that the bit error is not minimized per the symbol error. It is because, while a physical error occurs between adjacent signal points, a Hamming distance between the signal points of the symbol is dependent on the other symbols of correlated symbols. Consequently, there is a problem that the six-phase phase modulation applied conventional coding such as gray coding has an inferior error rate characteristic. As for the six-phase phase modulation, the encoding method for minimizing a bit error per symbol error is yet to be clarified.
Thus, an object of the present invention is to provide the modulation and demodulation system, modulator, demodulator and phase modulation method and phase demodulation method used therefor capable of solving the problem and minimizing the bit error rate in the six-phase phase modulation method.
Another object of the present invention is to provide the modulation and demodulation system, modulator, demodulator and phase modulation method and phase demodulation method used therefor capable of simplifying a circuit configuration in the six-phase phase modulation method.